In this study, we investigated electrocardiographic findings and evaluated whether the low QRS voltage provides prognostic information in patients with sepsis. Our findings suggest that sepsis patients with low QRS voltage had more severe organ dysfunction and higher mortality than those without low QRS voltage. Furthermore, low QRS voltage remained a significant prognostic factor for hospital mortality in the multivariable logistic regression model.
To the best of our knowledge, this is the first study suggesting the prognostic value of low QRS voltage in patients with sepsis. Our results are in line with previous studies showing that patients with low QRS voltage have more severe disease status and experience cardiovascular events more frequently than patients without low QRS voltage in cardiovascular disease 7–9. Because ECG is produced by electrodes on the body surface sensing the direction and magnitude of a wavefront of electrical activity generated by the heart, low QRS voltage can be seen in various medical conditions with impaired voltage potential generation from the myocardium, or with the increase in the transfer impedance of electrical signals from the heart to the electrodes 13,14. In other words, a low QRS voltage can be interpreted as a signal indicating that the patient is in a state of having decreased electrogenesis due to considerable myocardial ischemic injury or impaired transmission of cardiac current due to body fluid accumulation, which can lead to poor clinical outcomes 15.
Compared to the low QRS voltage found in about 1% of healthy lean individuals without comorbidities, the incidence was much higher in our sepsis cohort 16,17. Although we could not identify the cause of low QRS voltage, there was no significant difference from the patients with normal QRS voltage in comorbidities such as obesity, cardiovascular disease, or chronic lung disease, which are well-known causes of attenuating the amplitude of the QRS voltage. It suggests the possibility that pathophysiological changes after sepsis influenced the occurrence of low QRS voltage rather than the patient's underlying medical condition prior to sepsis. Activation of inflammation and coagulation in response to infection can lead to organ dysfunction, thus playing an important role in the pathogenesis of sepsis 18. In sepsis, a low QRS voltage may represent a proinflammatory and procoagulatory state. Szewieczek et al. reported that the amplitude of the QRS voltage was negatively correlated with the interleukin 6, tumor necrosis factor-alpha, and plasminogen activator inhibitor-1 19. Given that increase in proinflammatory cytokines and plasminogen activator inhibitor-1 during sepsis are associated with high mortality, we speculate that pathophysiological changes causing to low QRS voltage may also contribute to the fatality 20,21.
Interestingly, the low QRS voltage group had significantly higher levels of NT-proBNP compared to the normal QRS voltage group in our study. NT-proBNP is a cardiac hormone synthesized and secreted mainly from the ventricles in response to myocardial wall stress. Therefore, NT-proBNP is used as a marker of cardiac dysfunction or fluid overload 15. During sepsis, cardiac function may be acutely impaired, even in patients without pre-existing risk factors for cardiovascular disease. Several animal studies identified a decrease in action potential due to a reduced sodium and calcium current in the sepsis model and suggested that these changes contribute to the development of sepsis-induced cardiomyopathy 22–24. Therefore, low QRS voltage may be caused by systolic or diastolic dysfunction of the heart in sepsis, as reported in patients with chronic heart failure, but this relationship has not yet been evaluated 9. In addition, fluid overload during initial resuscitation may also result in low QRS voltage in sepsis. Madias et al. showed that intracardiac ECG did not change while the QRS amplitude of surface ECG changed according to the change in body weight in patients with sepsis, suggesting that fluid retention may be the main cause of low QRS voltage rather than impaired electrogenesis 25. However, in our study, since the median interval between the first recognition of sepsis and ECG recording was as short as 24 minutes, it seems difficult to explain the cause of high NT-proBNP and low QRS voltage only with fluid overload.
Several limitations to this study should be noted. First, because this study was conducted as an observational study design, there is a potential risk of various biases and confounding. Second, we only collected ECG data recorded at the time of diagnosis of sepsis. Therefore, it is impossible to distinguish whether the low QRS voltage identified at the diagnosis of sepsis was present before sepsis or a new finding after sepsis. And the association between the changes in the amplitude of QRS voltage that occurred during the course of sepsis treatment and the mortality was not evaluated. Third, the cause of low QRS voltage was not identified in our study. In particular, since echocardiography or hemodynamic monitoring was not routinely performed in our practice, it could not be determined whether the changes in QRS voltage were related to changes of the cardiovascular system during sepsis.
In patients with sepsis, a low QRS voltage identified early in diagnosis is associated with poor prognosis. Therefore, physicians should carefully monitor for symptoms and signs of clinical deterioration in patients with a low QRS voltage at diagnosis of sepsis. Further studies should be conducted to identify the underlying mechanism that leads to low QRS voltage and to evaluate whether the low QRS voltage can be used not only as a prognostic factor but also as a tool for monitoring the effectiveness of therapeutic interventions during sepsis.